Thermoplastic polyurethane elastomers from polyoxypropylene polyoxyethylene block copolymers

ABSTRACT

Polyurethane polyether-based elastomers are described which are thermoplastic, recyclable and have increased high temperature resistance which permits fabrication by injection molding. The elastomers are the product of reaction of 4,4&#39;-methylenebis(phenyl isocyanate), a particular group of polypropylene oxide-polyethylene oxide block copolymers and an extender [straight chain aliphatic diols C 2-6  or the bis(2-hydroxyethyl ether) of hydroquinone or resorcinol]. The block copolymers have at least 50 percent primary hydroxyl groups, a pH in the range of 4.5 to 9, a content of alkali metal ion less than 25 ppm and a molecular weight of 1000 to 3000. The minimum ethylene oxide (E.O.) residue content (percent by weight) of the polyether for any molecular weight (M.W.) is governed by the equation: ##EQU1## In a particularly preferred embodiment the elastomers are prepared by replacing up to 25 percent by equivalents of the extender by certain diols (polyethylene glycols up to 1500 M.W. preferred).

This application is a continuation-in-part of copending application Ser.No. 504,183, filed September 9, 1974, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to polyurethane elastomers and is moreparticularly concerned with thermoplastic polyurethane elastomersderived from polyether polyols and with methods for their preparation.

2. Description of the Prior Art

The preparation of thermoplastic polyurethane elastomers from polyesterpolyols is well-known in the art. Such elastomers can be extruded,injection molded and fabricated in other known manner without sufferingany degradation due to momentary exposure to the relatively highprocessing temperatures (of the order of 400° F.) involved in suchtechniques. In contrast, it has not hitherto been possible to usepolyethylene and polypropylene glycols to prepare thermoplasticpolyurethanes, which can be molded by techniques involving processingtemperatures of the above order. It is highly desirable that suchpolyurethanes be prepared since polyethylene and polypropylene glycolsare significantly less expensive than polyester polyols and therebywould provide obvious economic advantages. The latter would be inaddition to the recognized advantage in hydrolytic stability of theresulting polyurethanes, which hydrolytic stability is associated withthe use of polyether polyols as opposed to polyester polyols.

Unfortunately it has been found hitherto that polyurethane elastomersprepared using polyether polyols, particularly polypropylene glycol, arenot capable of withstanding exposure to temperatures of the order of400° F. even for a brief period such as that required in injectionmolding and like techniques.

We have now found that, by using a particular group of block copolymerpolyether glycols which have not hitherto been regarded as potentialcandidates for polyols in the preparation of polyurethane elastomers, itis possible to prepare thermoplastic polyurethane elastomers which willwithstand temporary exposure for limited periods to temperatures as highas 450° F. These elastomers can be fabricated readily, withoutdegradation, by extrusion, injection molding and the like. This findingresults in marked advantages in terms of reduction in cost as well asthe ability to use the more hydrolytically stable polyether basedpolyurethane elastomers for fabrication of articles by injection moldingand the like.

SUMMARY OF THE INVENTION

This invention comprises thermoplastic recyclable polyurethaneelastomers which are the product of reaction of:

(a) 4,4'-methylenebis(phenyl isocyanate),

(b) a polyoxypropylene polyoxyethylene block copolymer having amolecular weight in the range of about 1000 to 3000, a pH within therange of 4.5 to 9, a primary hydroxyl content of not less than 50percent, and a content of alkali metal ion not greater than 25 ppm, saidblock copolymer having a minimum content of ethylene oxide (E.O.)residues for any given molecular weight (M.W.) corresponding to:##EQU2##

(c) an extender selected from the class consisting of aliphatic straightchain diols from 2 to 6 carbon atoms, inclusive, and thebis(2-hydroxyethyl)ethers of hydroquinone and resorcinol, and mixturesthereof.

The invention also comprises polyurethanes as defined above in which upto 25 percent, on an equivalent basis, of the extender is replaced by adiol selected from the class consisting of (i) branched chain aliphaticdiols from 3 to 6 carbon atoms, (ii) diethylene glycol, dipropyleneglycol, (iii) polyethylene glycols having a molecular weight from 200 to1500, (iv) polycarprolactone diols having a molecular weight from 500 to3000, (v) polypropylene glycols having a molecular weight from 400 to1000 and (vi) polytetramethylene glycols having a molecular weight from650 to 1500, and (vii) mixtures of two or more of said diols andglycols.

The polyurethane elastomers of the invention are thermoplastic andsufficiently resistant to temporary exposure to temperatures of theorder of 400° F. as to permit fabrication by injection molding and liketechniques into articles such as automobile parts and accessories,containers, tubing, and the like, for which only polyester-basedpolyurethane elastomers have been used heretofore. The polyurethaneelastomers possess the hydrolytic stability commonly exhibited bypolyether-based polyurethanes as well as excellent structural strengthand stability characteristics. In addition the polyurethane elastomersof the invention are recyclable, i.e. when any article fabricated fromsaid elastomers is found to be below specification for any reason, saidarticle is not discarded but the material therein can be recycled bycomminuting and remolding. Similary, any scrap elastomer, such asflashing, generated in the molding process can be recycled and need notbe discarded.

The term "aliphatic straight chain diols from 2 to 6 carbon atoms,inclusive," means diols of the formula HO(CH₂)_(n) OH wherein n is 2 to6 and there is no branching in the aliphatic chain separating the OHgroups. The term is inclusive of ethylene glycol, 1,3-propanediol,1,4-butanediol, 1,5 -pentanediol and 1,6-hexanediol.

The term "branched chain aliphatic diols from 3 to 6 carbon atoms" meansan aliphatic diol having the stated carbon atom content in which thehydrocarbon chain separating the two hydroxyl groups is branched, i.e.the chain is substituted by at least one alkyl group. The term isinclusive of 1,2-propanediol, 1,3-butanediol, 2,3-butanediol,1,3-pentanediol, 1,2-hexanediol, 3-methylpentane-1,5-diol and the like.

The term "alkali metal ion" is inclusive of sodium, potassium, andlithium ions.

DETAILED DESCRIPTION OF THE INVENTION

The thermoplastic polyurethane elastomers of the invention can beprepared by processes which are conventional in the art for thesynthesis of polyurethane elastomers. Such processes include theone-shot procedure in which all the reactants are brought togethersimultaneously, and the prepolymer procedure in which the isocyanate isreacted with the polyol in a first-step and the isocyanate-terminatedprepolymer so produced is subsequently reacted with the extender. Theone-shot process includes the process in which the diisocyanate has beenconverted to a quasi-prepolymer by reaction with a very minor (i.e. lessthan about 10 percent on an equivalent basis) of polyol prior tocarrying out the polyurethane forming reaction. The one-shot is thepreferred procedure for preparing the elastomeric polyurethanes of theinvention. In a most preferred embodiment the elastomeric polyurethanesof the invention are prepared by a continuous one-shot procedure such asthat set forth in U.S. Pat. No. 3,642,964.

The principal feature which distinguishes the elastomeric polyurethanesfrom prior elastomers lies in the employment of a particular group ofpolyether diols. The latter are polyoxypropylene polyoxyethylene blockcopolymeric glycols which are obtained by first polymerizing propyleneoxide and then reacting the resulting polyoxypropylene glycol withethylene oxide. The reactions in question are carried out in accordancewith procedures well-known in the art; see, for example, U.S. Pat. No.2,674,619 which gives specific details of procedures of this type. Forexample, the polymerization of the propylene oxide is effected bycondensing propylene oxide with propylene glycol or water in thepresence of a basic catalyst such as sodium hydroxide, potassiumhydroxide and the like. The polymerization can be carried out to anydesired extent depending upon the desired molecular weight of theultimate product. The polypropylene oxide so obtained is then reactedwith ethylene oxide, also in the presence of a basic catalyst if sodesired.

The polyoxypropylene polyoxyethylene block copolymeric glycols of theinvention meet a number of very specific requirements. The molecularweight thereof lies within the range of 1000 to 3000. The proportion ofethylene oxide residues in the block copolymers must exceed a certainminimum which varies depending upon the molecular weight of the blockcopolymer under consideration. Thus, for a copolymeric glycol having agiven molecular weight (MW) the minimum amount, in percentage by weight,of ethylene oxide residues present in the gylcol is given by theequation (I) supra. Illustratively, the following minimum amounts ofethylene oxide units in the glycol are called for by the equation (I)for various molecular weights within the above range.

    ______________________________________                                        Molecular weight of glycol                                                                     % by weight of ethylene oxide                                ______________________________________                                        1000             7.5                                                          1200             18.75                                                        1400             26.78                                                        1600             32.81                                                        1800             37.5                                                         2000             41.25                                                        2200             44.32                                                        2400             46.87                                                        2600             49.04                                                        2800             50.89                                                        3000             52.5                                                         ______________________________________                                    

Further, whatever the molecular weight, the number of primary hydroxylgroups present in the block copolymeric glycols must be at least about50 percent. The majority of the primary hydroxyl groups are thosederived from the ethylene oxide residues but certain of the hydroxylgroups derived from propylene oxide can also be primary depending uponthe manner in which the oxirane ring of the propylene oxide opened up inthe polymerization. Accordingly, the percentage of primary hydroxylgroups present in a given block copolymeric glycol is not necessarilyrelated directly to the amount of ethylene oxide residues which havebeen introduced. The two parameters, namely, the percentage of primaryhydroxyl groups and the percentage by weight of ethylene oxide residues,are indicative of different characteristics of the block copolymericglycols and are not merely different ways of expressing the samecharacteristic.

In order to be useful in preparing the elastomeric polyurethanes of theinvention the block copolymeric glycols must be substantially free fromany remaining traces of basic catalyst employed in their manufacture. Bythis is meant the following. Advantageously the pH of the glycols iswithin the range of 4.5 to 9.0 and, preferably, is within the range of6.0 to 7.5. The amount of alkali metal ion present in the glycols isadvantageously less than about 25 ppm and preferably less than about 5ppm. Levels of alkali metal ion in excess of about 25 ppm give rise toundesirable results due to a significant level of trimerization of thediisocyanate during the polyurethane forming reaction.

In addition to meeting the above requirements, the polyoxypropylenepolyoxyethylene block copolymers employed in preparing the polyurethaneelastomers of the invention preferably also exhibit unsaturation of lessthan 0.06 milliequivalents/gram as measured by ASTM D 1638-60T andpreferably also exhibit a peroxide content of less than 15 ppm.

The polyoxypropylene polyoxyethylene block copolymers described abovehave been employed hitherto as surfactants and cell control agents inpolyurethane foam forming reactions. To the best of our knowledge it hasnot previously been suggested that these materials would be useful inthe preparation of polyurethane elastomers. It has certainly not beensuggested that these materials would give rise to polyurethaneelastomers having the particularly useful properties described herein.

The various diols employed as extenders in the preparation of thepolyurethane elastomers of the invention are well-known in the art as isthe diisocyanate which is employed.

The proportions in which the diisocyanate, the polyoxypropylenepolyoxyethylene block copolymers, and the extender are employed in thepreparation of polyurethane elastomers of the invention are such thatthe ratio of equivalents of isocyanate to total equivalents of hydroxylgroups in the reaction mixture is within the range of about 1:0.96 toabout 1:1.10. The relative proportions of polyoxypropylenepolyoxyethylene block copolymer to extender can vary over a wide rangedepending upon the molecular weight of the copolymer. In general theproportion of equivalents of copolymer to equivalents of extender iswithin the range of about 1:1 to about 1:12. It is found that the higherproportions of extender are desirable for the higher molecular weightcopolymers.

The hardness of the polyurethane elastomers of the invention lies withinthe range of about 60 Shore A to about 80 Shore D. In general, hardnessis a function of the molecular weight of the polyoxypropylenepolyoxyethylene copolymer; for any given ratio of equivalents ofextender and copolymer it is found that the higher the molecular weightof the copolymer the softer the elastomer.

As set forth above, the polyurethane elastomers of the invention arepreferably made by the one-shot procedure and most preferably by acontinuous one-shot procedure. In such procedures the reactants arebrought together in any order. Advantageously, the polyols, i.e. thepolyoxypropylene polyoxyethylene block copolymer and the extender(s),are preblended and fed to the reaction mixture as a single component,the other major component being the diisocyanate (or quasi-prepolymerwhere used). The mixing of the reactants can be accomplished by any ofthe procedures and apparatus conventional in the art. Preferably theindividual components are rendered substantially free from the presenceof extraneous moisture using conventional procedures; for example, byazeotropic distillation using benzene, toluene, and the like, or byheating under reduced pressure at a temperature above the boiling pointof water at the pressure employed.

The mixing of the reactants can be carried out at ambient temperature(of the order of 25° C.) and the resulting mixture is then heated to atemperature of the order of about 40° C. to about 130° C., preferably toa temperature of about 90° C. to about 120° C. Alternatively, andpreferably, one or more of the reactants is preheated to a temperaturewithin the above ranges before the admixing is carried out.Advantageously, in a batch procedure, the heated reaction components aresubjected to degassing in order to remove entrained bubbles of air orother gases before the reaction takes place. This degassing isaccomplished conveniently by reducing the pressure under which thecomponents are maintained until no further evolution of bubbles occurs.The degassed reaction components are then admixed and transferred tosuitable molds or extrusion equipment or the like and cured at atemperature of the order of about 20° C. to about 115° C. The timerequired for curing will vary with the temperature of curing and alsowith the nature of the particular composition. The time required in anygiven case can be determined by a process of trial and error.

It is frequently desirable but not essential, to include a catalyst inthe reaction mixture employed to prepare the compositions of theinvention. Any of the catalysts conventionally employed in the art tocatalyze the reaction of an isocyanate with a reactive hydrogencontaining compound can be employed for this purpose; see, for example,Saunders et al., Polyurethanes, Chemistry and Technology, Part I,Interscience, New York, 1963, pages 228-232; see also Britain et al., J.Applied Polymer Science, 4, 207-211, 1960. Such catalysts includeorganic and inorganic acid salts of, and organometallic derivatives of,bismuth, lead, tin, iron, antimony, uranium, cadmium, cobalt, thorium,aluminum, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper,manganese and zirconium, as well as phosphines and tertiary organicamines. Representative organotin catalysts are stannous octoate,stannous oleate, dibutyltin dioctoate, dibutyltin diluarate, and thelike. Representative tertiary organic amine catalysts are triethylamine,triethylenediamine, N,N,N',N'-tetramethylethylenediamine,N,N,N',N'-tetraethylethylenediamine, N-methylmorpholine,N-ethylmorpholine, N,N,N',N'-tetramethylguanidine,N,N,N',N'-tetramethyl-1,3-butanediamine, N,N-dimethylethanolamine,N,N-diethylethanolamine, and the like. The amount of catalyst employedis generally within the range of about 0.02 to about 2.0 percent byweight based on the total weight of the reactants.

When the compositions of the invention are prepared by the lesspreferred prepolymer method, the diisocyanate and the polyoxypropylenepolyoxyethylene glycol are reacted, if desired, in the presence of acatalyst as defined above, in a preliminary stage to form anisocyanate-terminated prepolymer. The proportions of diisocyanate andpolyoxypropylene polyoxyethylene glycol employed in the preparation ofthis prepolymer are consistent with the ranges defined above. Thediisocyanate and the polyoxypropylene polyoxyethylene glycol arepreferably rendered substantially free from the presence of extraneousmoisture, using the methods described above, before the formation of theprepolymer is carried out. The formation of the prepolymer isadvantageously carried out at a temperature within the range of about70° C. to about 130° C. under an inert atmosphere such as nitrogen gasin accordance with conventional procedures. The prepolymer so formed canthen be reacted, at any desired time, with the extender diol to form theelastomers of the invention. This reaction is carried out advantageouslywithin the range of reaction temperatures specified above for theone-shot procedure. In general, the prepolymer and the extender aremixed and heated within the requisite temperature range while themixture is degassed as described previously. The degassed mixture isthen transferred to a suitable mold, extrusion apparatus, or the like,and cured as described for the one-shot procedure.

If desired, the elastomers of the invention can have incorporated inthem, at any appropriate stage of preparation, additives such aspigments, fillers, lubricants, stabilizers, antioxidants, coloringagents, fire retardants, and the like, which are commonly used inconjunction with polyurethane elastomers.

In a particular embodiment of the invention it is found that up to about25 percent, based on equivalents, of the extender (c) can be replaced bya different diol without affecting the highly desirable properties ofthe elastomers of the invention. On the contrary, such replacementconfers enhanced resistance to high temperatures on the polyurethaneelastomers of the invention without detracting from the other desirableproperties. Illustrative of the diols which are used to replace aproportion of the extender (c) in the above manner are: diethyleneglycol, dipropylene glycol; branched chain aliphatic diols from 3 to 6carbon atoms, such as 1,2-propylene glycol, 1,3-butanediol, and3-methyl-1,5-pentane diol; N-methyldiethanolamine,N-ethyldiethanolamine; polyethylene glycols having molecular weights inthe range of 200 to 1500; polypropylene glycols having a molecularweight from 400 to 1000, polytetramethylene glycols having a molecularweight from 650 to 1500; and polycaprolactone diols having a molecularweight in the range of 500 to 3000.

In a preferred group of elastomers of the invention the extender (c) is1,4-butanediol of which from 3% to 10%, on an equivalent basis, has beenreplaced by dipropylene glycol, diethylene glycol,3-methyl-1,5-pentanediol, polyethylene glycol having a molecular weightof about 400 or mixtures thereof.

Where part of the extender (c) is replaced by another diol as describedabove, the latter can be added to the polyurethane forming reactionmixture as a separate component or can be preblended with the polyolcomponents as described previously.

The following examples describe the manner and process of making andusing the invention and set forth the best mode contemplated by theinventors of carrying out the invention but are not be be construed aslimiting.

EXAMPLE 1

A series of polyurethane elastomers was prepared, using a standardprocedure throughout, from a number of different polyoxypropylenepolyoxyethylene block copolymers having varying ethylene oxide contentsand primary hydroxyl contents but all having a molecular weight of 2000.The ethylene oxide content of all the polyols was determined by nuclearmagnetic resonance spectroscopy as described in Dow Chemical CompanyBulletin Method TC-AM-66-23 dated May 23, 1966. In all cases thepolyisocyanate used was 4,4'-methylenebis(phenyl isocyanate) and theextender was 1,4-butanediol. The procedure for preparation of theelastomers was as follows:

The polyoxypropylene polyoxyethylene block copolymer was degassed byheating under reduced pressure at 110° C. for 30 minutes. To theresulting material was added the 1,4-butanediol and the mixture soobtained was again degassed at 110° C. under reduced pressure for 30minutes. To the resulting product, still at 110° C., was added 0.024percent (by weight of total reactants) of stannous octoate followed bythe 4,4'-methylenebis(phenyl isocyanate). The mixture so obtained wassubjected to high speed mechanical stirring for 15 seconds and thenpoured into a shallow aluminum tray. The poured elastomer and tray wereallowed to stand at room temperature (circa 20° C.) for 24 hours.Thereafter the elastomer was chopped into pieces, granulated and driedfor 3 hours at 110° C. The dried material was then injection molded toform a sheet (4.5×4.5×1/16") for test purposes. The resulting sheet waspostcured for 16 hours at 115° C. followed by 7 days at room temperature(circa 20° C.). The cured elastomer was then subjected to physicaltesting.

In Table I below are recorded the proportions (in moles) of ingredientsempolyed in preparing the various elastomers in accordance with theabove process together with physical properties of the postcured pressedsheets derived from those elastomers which could be molded. The Tablealso records the behaviour of the various elastomers subjected tomolding temperatures from 350° F. to 450° F. In the case of ElastomersA-D, all of which are outside the scope of the invention, molding wasnot possible because of degradation at the molding temperatures.

                                      TABLE I                                     __________________________________________________________________________    Elastomer     A  B  C  D  E     F     G     H     I                           Polyol        1  2  3  4  5     6     6     7     8                           __________________________________________________________________________    % E.O.        0  10 12 11.16                                                                            46    47    47    27    10                          % Primary OH  8  63 52 53 81    84    84    75    63                          Metal ppm     -- -- 75 -- >15   <15   <15   --    --                          pH            7  7  7.8                                                                              8.7                                                                              7     7     7     7     7                           Proportions (molar)                                                           MDI           5.94                                                                             5.94                                                                             5.94                                                                             5.94                                                                             5.94  5.94  5.94  4.45  3.46                        Polyol        1  1  1  1  1     1     1     1                                 1,4-butanediol                                                                              5  5  5  5  5     5     4.5   3.5   2.5                         Dipropylene glycol                                                                          -- -- -- -- --    --    0.5   --    --                          NCO/OH        0.99                                                                             0.99                                                                             0.99                                                                             0.99                                                                             0.99  0.99  0.99  0.99  0.99                        Molding Temperature (°F.)                                              (time of exposure)                                                            350           d  d  d  OK OK    OK    OK    OK    OK                          380           e  e  e  OK ↓                                                                            ↓                                                                            ↓                                                                            ↓                                                                            ↓                    390           g  g  g  d  ↓ 5 min.                                                                     ↓ 15 min.                                                                    ↓ 20 min.                                                                    ↓  10                                                                        ↓ 10 min.            400           r  r  r  e  ↓ at                                                                         ↓ at                                                                         ↓ at                                                                         ↓ at                                                                         ↓ at                 410           a  a  a  g  ↓ 420° F.                                                             ↓ 420° F.                                                             ↓ 420° F.                                                             ↓ 420° F.                                                             ↓ 420°                                                          F.                          420           d  d  d  r  ↓                                                                            ↓                                                                            ↓                                                                            ↓                                                                            ↓                    440           e  e  e  a  ↓                                                                            ↓                                                                            ↓                                                                            ↓                                                                            ↓                    450           s  s  s  d  ↓                                                                            ↓                                                                            ↓                                                                            ↓                                                                            ↓                                           e  ↓                                                                            ↓                                                                            ↓                                                                            ↓                                                                            ↓                                           s  ↓                                                                            ↓                                                                            ↓                                                                            ↓                                                                            ↓                    Properties                                                                    Hardness      -- -- -- -- 44D   43D   --    92A   90A                         Modulus psi   -- -- -- -- 1120  900   --    790   730                         50%                                                                           100%          -- -- -- -- 1410  1010  --    1010  910                         300%          -- -- -- -- 2550  1820  --    1200  1180                        Tensile Strength: psi                                                                       -- -- -- -- 5120  4610  --    3240  2950                        Elongation at break: %                                                                      -- -- -- -- 510   550   --    --    --                          Compression set: %                                                                          -- -- -- -- 26.3  30.5  --    --    --                          Clash-Berg Modulus T.sub.f °C.                                                       -- -- -- -- -41   -40   --    --    --                          __________________________________________________________________________

Identity of polyols used in Elastomers of Table I (All polyols derivedby reacting a polyoxypropylene glycol with the appropriate quantity ofethylene oxide):

    ______________________________________                                        Polyol 1:  P2010         Union Carbide                                        2:         L61           Wyandotte                                            3:         X423          Olin                                                 4:         XD8379        Dow                                                  5:         L-44          Wyandotte                                            6:         X-427         Olin                                                 7:         L-42          Wyandotte                                            8:         L-31          Wyandotte                                            ______________________________________                                    

Polyol 5 was treated by filtration through Brightsorb clay before use.

EXAMPLE 2

Using the same standard procedure described in Example 1 a series ofelastomers was prepared with a varying ratio of polyol to 1,4-butanediolextender, using as the polyol in all cases the polyoxypropylenepolyoxyethylene copolymer having a molecular weight of 2200, an ethyleneoxide content of 46% by weight, a primary hydroxyl content of 81%, analkali metal content of circa 10 and a pH of 7. The proportions (moles)of ingredients and properties of the elastomers are summarized in TableII. Each of the elastomers could be maintained at the moldingtemperature of 420° F. for 10 minutes without showing any sign ofdegradation.

                  TABLE II                                                        ______________________________________                                        Elastomer         J      K      L    M    N                                   ______________________________________                                        MDI               4.08   5.10   6.12 7.14 8.16                                Polyol            1      1      1    1    1                                   1,4-butanediol    3      4      5    6    7                                   NCO/OH            1.02   1.02   1.02 1.02 1.02                                Molding temp. °F.                                                                        420    420    430  440  440                                 Hardness                                                                      Shore A           76     84     88   92   92                                  Shore D           25     31     39   42   45                                  Modulus: psi                                                                  100%              510    760    1000 1250 1510                                200%              710    1000   1290 1630 1910                                300%              900    1210   1620 2040 2560                                Tensile Strength psi                                                                            2470   2890   3930 5030 5580                                Elongation at break %                                                                           940    870    730  710  630                                 Tensile set at break: %                                                                         170    180    140  140  120                                 Tear Strength: Die C: psi                                                                       440    480    610  670  720                                 Compression set: %                                                                              40.3   41.2   35.7 40.8 41                                  Clash-Berg modulus, T.sub.f, °C.                                                         -56    -53    -49  -46  -42                                 ______________________________________                                    

EXAMPLE 3

A series of elastomers was prepared, using the procedure described inExample 1, from 4,4'-methylenebis(phenyl isocyanate) (MDI), thepolyoxypropylene polyoxyethylene glycol identified as Polyol 6 inExample 1, and 1,4-butanediol, but replacing 5 percent, on an equivalentbasis, of the butanediol by a second diol extender. The proportions(moles) of ingredients, and the properties of the resulting elastomers(after curing as described in Example 1) are set forth in Table IIIbelow.

                  TABLE III                                                       ______________________________________                                        Elastomer         O        P        Q                                         ______________________________________                                        MDI               6.12     6.12     6.12                                      Polyol 6          1        1        1                                         1,4-butanediol    4.75     4.75     4.75                                      dipropylene glycol                                                                              0.25     --       --                                        diethylene glycol --       0.25     --                                        3-methyl-1,5-pentanediol                                                                        --       --       0.25                                      NCO/OH            1.02     1.02     1.02                                      Properties                                                                    Hardness                                                                      Shore A           82       86       --                                        Shore D           40       40       --                                        Modulus psi                                                                   50%               780      900      800                                       100%              1170     1270     1200                                      300%              2510     2340     2150                                      Tensile strength: psi                                                                           5250     4370     4250                                      ______________________________________                                    

EXAMPLE 4

A series of elastomers was prepared, using the procedure described andingredients in Example 1 but replacing 1,4-butanediol by varying amountsof bis(2-hydroxyethyl ether) of hydroquinone as extender and using asthe polyoxypropylene polyoxyethylene glycol, one having a % E.O. contentof 52, a % primary hydroxyl content of 83, and a pH of 7 [L-35:Wyandotte]. The proportions (moles) of ingredients and properties of theelastomers (after curing as described in Example 1) are set forth inTable IV below.

                  TABLE IV                                                        ______________________________________                                        Elastomer          R        S       T                                         ______________________________________                                        MDI                2.575    3.605   4.635                                     Polyoxypropylene polyoxy-                                                                        1        1       1                                         ethylene glycol                                                               Bis(2-hydroxyethyl ether)-                                                                       1.5      2.5     3.5                                       hydroquinone                                                                  NCO/OH             1.03     1.03    1.03                                      Properties                                                                    Hardness                                                                      Shore A            80       90      94                                        Shore D            --       42      50                                        Modulus psi                                                                   50%                500      900     1200                                      100%               700      1200    1600                                      300%               1000     1700    2390                                      Tensile strength: psi                                                                            2850     3200    3250                                      ______________________________________                                    

EXAMPLE 5

Using the procedure described in Example 1, an elastomer was preparedfrom the following ingredients and proportions (all proportions inmoles);

    ______________________________________                                        MDI                   7.55 moles                                              Polyol.sup.1          1.0 moles                                               1,4-butanediol        6.0 moles                                               Polyethylene glycol   0.4 moles                                               (M.W. = 400)                                                                  NCO/OH = 1.02:1                                                               ______________________________________                                         .sup.1 Same as Polyol 5 (Example 1)                                      

The elastomer, after forming into pressed sheets and curing as describedin Example 1, was found to have the following properties:

    ______________________________________                                        Density                1.185 g/cc.                                            Shore D Hardness       40                                                     Modulus psi                                                                   at 100%                1290                                                   300%                   2240                                                   Tensile Strength: psi  5540                                                   Elongation at break %  480                                                    Elongation set %       55                                                     Compression set %      33                                                     Clash-Berg Modulus T.sub.f °C.                                                                -37                                                    ______________________________________                                    

The elastomer was injection molded to form the pressed sheet for testingpurposes and showed no tendency to degrade in the molding process.

EXAMPLE 6

Using the procedure described in Example 1, an elastomer was preparedfrom the following ingredients and proportions (in moles):

    ______________________________________                                        MDI                   7.45 moles                                              Polyol.sup.1          1.0 mole                                                1,4-butanediol        6.0 moles                                               Polyethylene glycol   0.3 mole                                                (M.W. = 400)                                                                  NCO/OH = 1.02:1                                                               ______________________________________                                         .sup.1 Same as Polyol 6 (Example 1)                                      

The elastomer, after forming into pressed sheets by injection moldingand curing as described in Example 1, was found to have the followingproperties:

    ______________________________________                                        Shore A Hardness        90                                                    Modulus psi                                                                   at 50%                  1140                                                  100%                    1350                                                  200%                    1850                                                  300%                    2380                                                  Tensile Strength: psi   5460                                                  Elongation at break %   540                                                   Elongation set %        60                                                    Compression set %       26                                                    ______________________________________                                    

The elastomer showed no sign of degradation on being injection molded.

EXAMPLE 7

Using the procedure described in Example 1, an elastomer was preparedfrom the following ingredients and proportions (moles):

    ______________________________________                                        MDI                   4.08 moles                                              Polyol.sup.1          0.75 moles                                              1,4-butanediol        3.0 moles                                               Polyethylene glycol   0.25 mole                                               (M.W. = 1000)                                                                 NCO/OH = 1.02:1.0                                                             ______________________________________                                         .sup.1 Same as Polyol 6 (Example 1)                                      

The elastomer, after forming into pressed sheets by injection moldingand curing as described in Example 1, was found to have the followingproperties:

    ______________________________________                                        Density                1.169 g/cc.                                            Shore A Hardness       80                                                     Modulus psi                                                                   at 50%                 460                                                    100%                   670                                                    200%                   960                                                    300%                   1250                                                   Tensile Strength: psi  4250                                                   Elongation at break %  730                                                    Tensile set %          90                                                     Compression set %      23                                                     Clash-Berg Modulus T.sub.f °C.                                                                -48                                                    ______________________________________                                    

The elastomer showed no sign of degradation on being injection molded.

EXAMPLE 8

An elastomer was prepared exactly as described in Example 7 except thatthe proportion of 1,4-butanediol to polyol was increased as follows:

    ______________________________________                                        MDI                     6.12                                                  Polyol 6                0.75                                                  1,4-butanediol          5.0                                                   Polyethylene glycol     0.25                                                  (M.W. = 1000)                                                                 ______________________________________                                    

The elastomer, in the form of injection molded sheets as described inExample 1, was found to have the following properties:

    ______________________________________                                        Density                1.196 g/cc.                                            Shore A Hardness       90                                                     Modulus psi                                                                   at 50%                 1040                                                   100%                   1400                                                   200%                   1920                                                   300%                   2540                                                   Tensile Strength: psi  5410                                                   Elongation at break %  520                                                    Elongation set %       60                                                     Tear Strength: pli     910                                                    Compression set %      29                                                     Clash-Berg Modulus T.sub.f °C.                                                                -39                                                    ______________________________________                                    

The stability of the above elastomer to processing temperatures of 400°F. encountered in injection molding was determined using a MonsantoRheometer in which a charge of the elastomer was maintained at 400° F.in the extruder barrel and, at intervals of five minutes, a fixed amountof material was extruded from the orifice under pressure of 90 psig andthe time taken to extrude this fixed amount of material was determined.The following results were recorded:

    ______________________________________                                                     Time taken to extrude                                            Elapsed time fixed amount                                                     ______________________________________                                         5 mins.     0.225 minutes                                                    10 mins.     0.201 minutes                                                    15 mins.     0.195 minutes                                                    20 mins.     0.255 minutes                                                    ______________________________________                                    

The above results indicate stability of the material to processing underextrusion conditions.

EXAMPLE 9

Using the procedure described in Example 1, an elastomer was preparedfrom the following ingredients and proportions (moles):

    ______________________________________                                        MDI                    12.12 moles                                            Polyol 5 (see Example 1)                                                                             1.0 mole                                               1,4-butanediol         10.0 moles                                             Polyethylene glycol    1.0 mole                                               (M.W. = 1500)                                                                 NCO/OH = 1.01/1.0                                                             ______________________________________                                    

The elastomer, after forming into pressed sheets by injection moldingand curing as described in Example 1, was found to have the followingproperties:

    ______________________________________                                        Hardness: Shore A        90                                                   Modulus psi                                                                   at 50%                   890                                                  100%                     1140                                                 200%                     1490                                                 300%                     1980                                                 Tensile Strength: psi    4490                                                 Elongation at break %    660                                                  Tensile set %            130                                                  Compression set %        37                                                   Clash-Berg Modulus T.sub.f °C.                                                                  -45                                                  ______________________________________                                    

The above elastomer showed no sign of degradation when injection moldedto form the pressed sheets for determination of the above properties.

EXAMPLE 10

Using the procedure described in Example 1, an elastomer was preparedfrom the following ingredients and proportions (moles):

    ______________________________________                                        MDI                      4.2 moles                                            Polyol 6 (see Example 1) 1.0 mole                                             Bis(2-hydroxyethyl)ether of                                                                            3.0 moles                                            resorcinol                                                                    NCO/OH = 1.05/1.0                                                             ______________________________________                                    

The elastomer so obtained was injection molded, without showing any signof degradation, to form pressed sheets which were cured as described inExample 1 and then found to have the following properties:

    ______________________________________                                        Density               1.18 g/cc.                                              Hardness: Shore A     89                                                      Tensile Modulus psi                                                           at 50%                900                                                     100%                  1190                                                    300%                  1570                                                    Tensile Strength, psi 2630                                                    Elongation at break % 690                                                     Tensile set %         90                                                      Compression set %     23                                                      ______________________________________                                    

EXAMPLE 11

Using the procedure described in Example 1, an elastomer was preparedfrom the following ingredients and proportions (moles):

    ______________________________________                                        MDI                    8.91 moles                                             Polyol.sup.1           1.0 mole                                               1,4-butanediol         7.14 moles                                             Polycaprolactone diol  0.43 mole                                              (M.W. = 2000)                                                                 NCO/OH = 1.04/1.0                                                             ______________________________________                                    

The elastomer so obtained was injection molded, without showing any signof degradation, to form pressed sheets which were cured as described inExample 1 and then found to have the following properties:

    ______________________________________                                        Hardness: Shore D       39                                                    Modulus, psi                                                                  at 50%                  1050                                                  100%                    1320                                                  300%                    2260                                                  Tensile Strength, psi   5660                                                  Elongation %            630                                                   Tensile set %           80                                                    Compression set %       43                                                    ______________________________________                                    

EXAMPLE 12

Using the procedure described in Example 1, two elastomers were preparedin which a minor part of the 1,4-butanediol extender was replaced bypolytetramethylene glycol (PTMG) having a molecular weight of 1000(Teracol 1000). The ingredients and molar proportions were as follows:

    ______________________________________                                        Elastomer          U          V                                               ______________________________________                                        MDI                7.58       6.93                                            Polyol 6 (see Example 1)                                                                         1.0        1.0                                             1,4-butanediol     6.25       5.55                                            PTMG               0.25       0.11                                            NCO/OH             1.01/1.0   1.04/1.0                                        ______________________________________                                    

The two elastomers were injection molded, without showing any signs ofdegradation, to form pressed sheets which were cured as described inExample 1 and then found to have the following properties:

    ______________________________________                                        Elastomer            U         V                                              ______________________________________                                        Density, g/cc.       1.18      1.18                                           Hardness: Shore A    88        87                                             Modulus, psi                                                                  at 50%               920       920                                            100%                 1340      1180                                           200%                 1930      1530                                           300%                 2660      1900                                           Tensile Strength, psi                                                                              5790      4930                                           Elongation at break %                                                                              480       640                                            Tensile set %        50        --                                             Elongation set %     --        110                                            Die C Tear Strength, psi                                                                           710       --                                             Compression set %    27        32.5                                           Clash-Berg Modulus T.sub.f °C.                                                              -38.5     -44                                            ______________________________________                                    

EXAMPLE 13

Using the procedure described in Example 1, an elastomer was prepared inwhich a minor part of the 1,4-butanediol extender was replaced bypolypropylene glycol (PPG) of molecular weight 1025. The ingredients andmolar proportions are as follows:

    ______________________________________                                        MDI                    6.86                                                   Polyol 6 (see Example 1)                                                                             1.0                                                    1,4-butanediol         5.55                                                   PPG                    0.11                                                   NCO/OH                 1.03/1.0                                               ______________________________________                                    

The elastomer was injection molded, without showing any signs ofdegradation, to form a pressed sheet which was cured as described inExample 1 and then found to have the following properties:

    ______________________________________                                        Density, g/cc.            1.18                                                Hardness: Shore A         87                                                  Modulus, psi                                                                  at 50%                    910                                                 100%                      1200                                                200%                      1600                                                300%                      2100                                                Tensile Strength, psi     5210                                                Elongation at break %     590                                                 Tensile set %             90                                                  Compression set %         31                                                  Clash-Berg Modulus T.sub.f °C.                                                                   -42                                                 ______________________________________                                    

We claim:
 1. A thermoplastic, recyclable polyurethane elastomer which isthe product of reaction of(a) 4,4'-methylenebis(phenyl isocyanate), (b)a polyoxypropylene polyoxyethylene block copolymer having a molecularweight in the range of about 1000 to 3000, a pH within the range of 4.5to 9, a primary hydroxyl content of not less than 50 percent and acontent of alkali metal ion not greater than 25 ppm, said blockcopolymer having a minimum content of ethylene oxide (E.O.) residues forany given molecular weight (MW) corresponding to: ##EQU3## (c) anextender consisting of from 75 to 100 percent, on an equivalent basis,of a member selected from the class consisting of aliphatic straightchain diols having from 2 to 6 carbon atoms, inclusive, and thebis(2-hydroxyethyl)ethers of hydroquinone and resorcinol, and mixturesthereof and from 25 to 0 percent by equivalents of a member selectedfrom the class consisting of (i) branched chain aliphatic diols from 3to 6 carbon atoms, (ii) diethylene glycol and dipropylene glycol, (iii)polyethylene glycols having a molecular weight from 200 to 1500, (iv)polycaprolactone diols having a molecular weight from 500 to 3000, (v)polypropyelene glycols having a molecular weight from 400 to 1000, (vi)polytetramethylene glycols having a molecular weight from 650 to 1500and (vii) mixtures of two or more of said diols or glycols; the molarproportions of said block copolymer (b) to said extender (c) beingwithin the range of about 1:1 to 1:12, and the ratio of equivalents ofisocyanate to total equivalents of hydroxyl groups being within therange of about 1:0.96 to about 1:1.10.
 2. A thermoplastic, recyclablepolyurethane elastomer according to claim 1 wherein the extender is1,4-butanediol.
 3. The thermoplastic, recyclable polyurethane elastomeraccording to claim 1 wherein the extender is a mixture comprising from100 to 75 percent, on an equivalent basis, of 1,4-butanediol and from 0to 25 percent by equivalents of dipropylene glycol.
 4. A thermoplastic,recyclable polyurethane elastomer according to claim 1 wherein theextender is a mixture comprising from 100 to 75 percent, on anequivalent basis, of 1,4-butanediol and from 0 to 25 percent byequivalents of polyethylene glycol having a molecular weight of about400.
 5. A thermoplastic, recyclable, polyurethane elastomer according toclaim 1 wherein the polyoxypropylene polyoxyethylene block copolymer hasa molecular weight of about 2000 and a minimum of 41.25 percent byweight of ethylene oxide residues.
 6. A thermoplastic, recyclable,polyurethane elastomer which is the product of reaction of:(a)4,4'-methylenebis(phenyl isocyanate); (b) a polyoxypropylenepolyoxyethylene block copolymer having a molecular weight in the rangeof about 2000, a pH within the range of 6.0 to 7.5, a primary hydroxylcontent of not less than 50 percent, a content of alkali metal ion notgreater than 25 ppm, a minimum content of ethylene oxide residues of40%; and (c) an extender consisting of from 75 to 100 percent, on anequivalent basis, of 1,4-butanediol, and from 25 to 0 percent byequivalents of a member selected from the class consisting of (i)branched chain aliphatic diols from 3 to 6 carbon atoms, (ii) diethyleneglycol and dipropylene glycol, (iii) polyethylene glycols having amolecular weight from 200 to 1500, (iv) polycaprolactone diols having amolecular weight from 500 to 3000, (v) polypropylene glycols having amolecular weight from 400 to 1000, (vi) polytetramethylene glycolshaving a molecular weight from 650 to 1500 and (vii) mixtures of two ormore of said diols or glycols.
 7. A thermoplastic, recyclable,polyurethane elastomer according to claim 6 wherein up to 25% of the1,4-butanediol is replaced by an equivalent amount of dipropyleneglycol.
 8. A thermoplastic, recyclable, polyurethane elastomer accordingto claim 6 wherein up to 25% of the 1,4-butanediol is replaced by anequivalent amount of diethylene glycol.
 9. A thermoplastic, recyclable,polyurethane elastomer according to claim 6 wherein up to 25% of the1,4-butanediol is replaced by an equivalent amount of polyethyleneglycol of molecular weight of about
 400. 10. A thermoplastic,recyclable, polyurethane elastomer according to claim 6 wherein up to25% of the 1,4-butanediol is replaced by an equivalent amount of3-methyl-1,5-pentanediol.
 11. A thermoplastic, recyclable, polyurethaneelastomer which is the product of reaction of:(a)4,4'-methylenebis(phenyl isocyanate); (b) a polyoxypropylenepolyoxyethylene block copolymer having a molecular weight in the rangeof about 2000, a pH within the range of 6.0 to 7.5, a primary hydroxylcontent of not less than 50 percent, a content of alkali metal ion notgreater than 25 ppm, a minimum content of ethylene oxide residues of40%; and (c) bis(2-hydroxyethyl ether) of hydroquinone, the molarproportions of (b) to (c) being within the range of about 1:1 to 1:12,and the ratio of equivalents of isocyanate to total equivalents ofhydroxyl groups being within the range of about 1:0.96 to about 1:1.10.12. A thermally stable polyurethane elastomer which is a reactionproduct of (a) a poly(oxypropylene)poly(oxyethylene) glycol of molecularweight from about 1000 to about 3000 and containing 15 to 50% by weightof oxyethylene groups (b) methylenebis(4-phenylisocyanate) and (c)1,4-butanediol; the NCO/OH equivalents ratio being from 0.96 to 1.10 andthe molar ratio of (c) to (a) being from 1/1 to 12/1, said elastomerhaving a hardness of about 40 to 55 Shore D, an elongation of greaterthan 270%, an ultimate tensile strength of at least 2700 psi and a Die Ctear strength of at least 500 pli, said elastomer displaying improvedthermal stability as evidenced by its ability to retain at least twiceas much of its original tensile strength, after exposure to atemperature of 415° F. for 20 minutes, as an otherwise similar elastomerin which (a) contains 10% or less oxyethylene groups.
 13. A thermallystable polyurethane elastomer as in claim 12 in which the molecularweight of (a) is about 2000 and the oxyethylene group content is 30-45%.14. A shaped article prepared from the thermally stable polyurethaneelastomer of claim
 12. .Iadd.
 15. A thermoplastically processiblepolyurethane prepared by reacting 4,4'-methylenebis(phenyl isocyanate),a low molecular weight glycol chain extender having only primaryhydroxyl groups and a blend of from about 25 to about 95 parts byweight, per 100 parts by weight of blend, of a block copolymer ofethylene oxide and 1,2-propylene oxide wherein the molecular weight ofthe copolymer is from about 1000 to about 3000, and the remainder of theblend is poly(tetramethylene ether)glycol having a molecular weight offrom about 650 to 1500, said block copolymer containing from about 60 toabout 100 percent primary hydroxyl groups. .Iaddend..Iadd.
 16. Thepolyurethane of claim 15 wherein the chain extender is 1,4-butanediol..Iaddend..Iadd.
 17. The polyurethane of claim 15 wherein the chainextender is bis-hydroxyethyl ether of hydroquinone. .Iaddend. .Iadd. 18.The polyurethane of claim 15 wherein the chain extender is diethyleneglycol.